1. Field of the Invention
The present invention relates to a ray emission device and an imaging system having the ray emission device.
2. Description of the Related Art
Scattering imaging is generally applied by scanning an object point by point with a modulated ray pencil beam while receiving the point scanning signals by a detector. Images reflecting information of the object is acquired by one-to-one correspondence between the scanning positions and the signals when processing data. The key point lies in a method by which the ray is modulated and constrained into a pencil beam and a flying spot scanning is achieved, in such application.
In a conventional flying spot scanning method, a rotary shield with one or more collimating holes is rotated in a sectorial scanning plane of the ray so that the ray is formed into a pencil beam for a flying spot by transmitting the ray through the one or more collimating holes, thereby achieving a scanning in a first dimensional direction. In order to effectively improve detection efficiency, a detector with a large area is needed to cover a solid angle of scattered rays formed when the pencil beam hits the object as far as possible. Generally, the detector is moved (translated or rotated) with the sectorial scanning plane of ray relative to the object under inspection, thereby achieving a scanning in a second dimensional direction. The relative movement may be such that the sectorial scanning plane of ray and the detector move while the object is stationary, or the sectorial scanning plane of ray and the detector are stationary while the object moves. A set of motor drive device is needed to rotate the rotary shield when carrying out a scanning in the first dimensional direction, while another set of motor drive device is required to move the ray generating device, the rotary shield and the detector together relative to the object when performing a scanning in the second dimensional direction.
As described above, two sets of mechanical drive devices are generally used to achieve a two-dimensional scanning in the prior art flying spot scanning method, and their real-time movement positions (or angles) are interrelated, and need accurate control. The two sets of mechanical drive devices have complicated mechanical structures. If the sectorial scanning plane of ray is rotated, then there is a further problem that the moment of inertia of the rotary shield is to be overcome.
Continuous movement of the scanning in the second dimensional direction will cause an actual scanning line in the first dimensional direction not to be parallel to a movement direction in the first dimensional direction with an angle of inclination between the actual scanning line and the movement direction, thereby finally causing geometry deformation of the scan images, and deteriorating the images. The more a speed of the scanning movement in the second dimensional direction is, the more the deformation is. On the other hand, the less the speed of the scanning movement in the second dimensional direction is, the longer the entire scanning time of the system is.
Therefore, there is a need for an improved flying spot scanning method which can effectively eliminate or alleviate the above dilemma.